This invention relates to a gear profile for an orbital gear transmission, an orbital gear transmission and winches such as deck winches for yachts and hoists for lifting heavy loads, which include orbital gear transmissions.
The transmission of power involving large torque loads through rotary machines is normally done by means of various gear systems. When large ratio reductions and accompanying torque conversion is required it is common practice to use either spur or planetary gear trains. These involve many elements and tend to be bulky. A worm and a wheel drive provides a simple alternative but because the gear engagement depends on sliding contact, these machines are very inefficient under large loads. Spur and planetary gears use gear teeth which operate in rolling contact by using gear teeth with their surfaces in the form of involutes. This produces highly efficient transmission.
Orbital gear systems, which operate by causing one gear with externally formed teeth to orbit while engaged about another while engaging teeth formed on its inner surface have been known for some time. It has been further known that such gear systems have the potential to provide very great reductions from relatively simple machines.
Unlike spur or epicycle planetary gear systems, where tooth engagement is predicted upon two cylinders rolling together upon their external surfaces, orbital gears cause one cylinder to roll on the inner surface of another. The teeth on spur gears or racks execute small epicycles on the surfaces of the cylinders and hence the engagement process is more or less tangential to the surfaces. This motion generates the involute surfaces of the teeth surfaces.
Orbital gears, on the other hand, execute cycloidal motion against the inner surface of the internal gear, and hence the engagement process is essentially radial and teeth with involute gear forms produce only sliding contact with high friction under load. Up until now this has made orbital gears little more than engineering curiosities.
In an attempt to make use of other important features of orbital gears some enterprises have tried to use simple cycloidal teeth forms. This form still produces sliding contact and although the incorporation of and array of bearings reduces this frictional problem it vastly increases the size and complexity of such machines which severely limits their use.
Clearly therefore a need exists to develop a new gear from which allows orbital gear systems to employ only rolling tooth contact while maintaining the fundamental principle of rigid body gear contact to ensure that their pitch circle roll together without slippage.
The first aspect of the invention may also be said to reside in an orbital gear system, including:
an inner gear and an outer gear;
the inner gear having a plurality of external teeth, the plurality of external teeth having a contact surface and a opposite surface, the inner gear having a pitch circle, the contact surface having a point of inflection located on the pitch circle of the first gear;
the outer gear having a plurality of internal teeth for engagement with the external teeth of the inner gear, the internal teeth having a contact surface for engaging the contact surface of the external teeth of the inner gear, the outer gear having a pitch circle; and
wherein, when the inner gear and outer gear are assembled for transmission of power from one of the gears to the other of the gears, the inner and outer gear undergo substatially radial engagement and point contact with the point of inflection of the external teeth engaging and rolling across an only point on the contact surface of the internal gear substantially where the pitch circle of the outer gear intersects the contact surface of the outer gear.
The first aspect of the invention also provides an orbital gear transmission including the orbital gear system.
The first aspect of the invention also provides a rotary transmission mechanism, including:
a first body having contact elements;
a second body having contact elements for engaging the contact elements of the first body and transferring rotary motion from the first body to the second body;
one of the first body or second body being arranged for orbital motion relative to the other of the first or second body; and
the elements of the first body and second body in contact with one another, when rotary motion is transferred, execute cupsoid cycloidal motion with respect to each other and engage radially by a rocking motion between the elements with one of the elements rocking on substantially a point of a surface of the other of the elements.
The first aspect of the present invention provides a gear profile which greatly improves the performance of orbital gear systems and orbital gear transmissions. The gear, system and transmission of this aspect of the invention abides by rolling gear principles but prevents slippage between pitch circles of the inner and outer gears. The rolling contact occurs at a point, for example approximately 4% of the cycle of each gear, but with orbital gear systems more gears are in engagement with one another. The present invention particularly enables orbital gears having pitch circles of very similar diameter. Since the contact occurs the pitch circles of the inner and outer gears very smooth operation of the gears. The sinusoid which forms part of the contact surface of the inner gear is related to two parameters of the system, namely the eccentricity of the orbital system and the diameter of the pitch circle for a given number of teeth. The gears may be made by sophisticated machines such as laser cutters or wire cutters but can also be made by shapers such as a Fellows shaper and tools such as a Hobb tool can be constructed on the principles for manufacture of such gears. Orbital gear systems using the teeth profile according to this aspect of the invention also enables very low reductions from simple machines and the ability to stop under load and remains stationary until the cycle is activated by the input to the transmission. Furthermore, the transmission is easily disengaged by release of an orbit control mechanism in the orbital system to effectively place the transmission into neutral.
Preferably the contact surface has a sinusoidal profile with the sinusoidal profile being defined by the following equation:
y=ƒ(D)Sin{xcfx80WDxcex8g(xcex5)}
where D is the diameter of the pitch circle
W is tooth width
xcex5 is eccentricity
xcex8 angular displacement
within the constraint the D of the inner gear is more than two thirds the D of the outer gear.
Preferably the external teeth of the inner gear are truncated having a generally flat outermost surface and the sinusoidal portion of the contact surface extends from a point radially inwardly of the pitch circle of the gear to the truncated surface.
Preferably the opposite surface of the external teeth are also provided with a sinusoidal profile along at least part of the length of the opposite surface. The sinusoidal profile of the opposite surface having a point of inflection located on the pitch circle of the gear, so that the gear can operate in both forward and reverse directions with the contact surface making contact with the internal teeth of the outer gear in one direction and the opposite surface effectively becoming the contact surface for rotation in the opposite direction.
Preferably the contact and opposite surfaces of the external teeth are a mirror image with respect to one another.
Preferably the contact surface of the internal gears is an inclined flat surface which extends from a radially outer point to the point where the pitch circle of the outer gear intersects with the contact surface.
Preferably the angle of the flat surface with respect to the radius of the outer gear is determined by the derivative of the sinusoid forming the sinusoidal profile of the external teeth at the point of inflection of the sinusoidal profile.
Preferably the contact surface of the internal teeth extends radially inwardly from the point of intersection of the contact surface and the pitch circle of the outer gear to a radially most inner point of the internal teeth.
Preferably the internal teeth have a opposite surface which is a mirror image of the contact surface with the opposite surface becoming the contact surface in reverse motion of the gear system.
A second aspect of the invention relates to an orbital gear transmission.
This aspect of the invention provides an orbital gear transmission, including:
an inner gear having a plurality of external teeth;
an outer gear having a plurality of internal teeth for engagement with the external teeth of the inner gear;
one of the inner or outer gears being mounted on an eccentric member;
orbit control means for engaging the inner or outer gear which is mounted on the eccentric member so as to control movement of the inner or outer gear mounted on the eccentric member to undergo orbital motion;
brake means for engaging the orbit control means and maintaining the orbit control means stationary so as to control orbital motion of the inner or outer gear mounted on the eccentric and wherein the brake means; and
means for releasing the brake to, in turn, release the orbit control means so that the orbit control means no longer controls orbital motion so the inner or outer gear can freely rotate to place the transmission into neutral.
This aspect of the invention provides a transmission for machines such as winches including hoists and deck winches for yachts which provide simple machines providing high efficiency and very low reductions.
The orbital control means may comprise an orbital control plate having openings or pins which engage with respectively pins or openings on the inner or outer gear which is mounted on the eccentric.
Preferably the inner and outer gears are configured according to the first aspect of the invention described above.
In other embodiments of the invention, the orbital control means may comprise a regressive control gear having gear teeth which engage control gear teeth provided on the inner or outer gear mounted on the eccentric. The regressive control gear enables regressive motion of the inner or outer gear which is mounted on the eccentric so that extremely low reductions can be provided.
Preferably the transmission according to the second aspect of the invention is provided in a winch.
In one embodiment, the winch is in the form of a hoist having an input pulley mounted on an input shaft which is coupled to the eccentric and an output pulley is coupled to the inner or outer gear which is not mounted on the eccentric so that drive is transmitted from the input pulley to the input shaft to the eccentric, to the inner or outer gear mounted on the eccentric and then to the inner or outer gear which is not mounted on the eccentric and then to the output pulley.
This aspect of the invention which is used in hoists has particular advantages and, in particular, that the orbital transmission can remain stationary when the input shaft is stopped by ceasing to pull on a chain or cable coupled to the input pulley so that the transmission and therefore the hoist will remain in a stationary position even when supporting a load until the chain on the input pulley is again pulled to activate the input and therefore the orbital transmission. By releasing the braking means after load is removed, the orbital transmission could be placed in neutral to thereby release the hoist.
In another embodiment, the orbital gear transmission may be included in a deck winch for a yacht, the eccentric being coupled to an input shaft which is rotated by a winch handle, the deck winch having a drum for receiving a rope to be drawn in or released by the winch, the drum being coupled to the input shaft by a first ratchet so that upon rotation of the input shaft in one direction, drive is transmitted via the ratchet to the drum to rotate the drum with a 1:1 gear ratio, the inner or outer gear which is not mounted on the eccentric member also being coupled to the drum by a second ratchet which freewheels when the input shaft is rotated in the first direction but which engages when the input shaft is rotated in the opposite direction so that drive is transmitted via the orbital gear transmission and the second ratchet to the drum to rotate the drum with a drive ratio according to the drive ratio of the orbital transmission, and with the first ratchet freewheeling when the input shaft is rotated in the opposite direction.
Thus, according to this aspect of the invention, the winch drum is always rotated in the same direction notwithstanding rotation of the input shaft in opposite directions.
Preferably the input shaft is mounted on a mast of the input shaft having a hollow for receiving the mast.
Once again, in this embodiment of the invention, the brake means can be released so as to release the orbital control means to place the transmission in neutral and thereby release the winch. Thus, if it is necessary to quickly release the deck winch so as to release a sail, the brake mechanism can simply be released to in turn release the orbital control means to place the transmission into neutral so that the drum can freewheel.
The invention also provides an orbital gear transmission including:
a first outer gear having a plurality of internal teeth;
a second outer gear having a plurality of internal teeth;
an input having an eccentric;
a first inner gear, having a plurality of external teeth, on the eccentric, the teeth of the first inner gear engaging the teeth of the first outer gear;
a second inner gear, having a plurality of external teeth, on the eccentric, the teeth of the second inner gear engaging the teeth of the second outer gear; and
an output coupled to the second outer gear.